With a recent marked improvement in the recording density in the field of magnetic recording, there have been increased needs for reduction in the track width for magnetic heads serving as an electromagnetic transducer element, intensified saturation magnetization of core materials, and improvement in permeability in the high frequency range of core materials.
Core members for a magnetic head have heretofore been fabricated by cutting ferrite or Fe-Si-Al material into a block and forming the block with grooves 3 for defining the track width 2 and grooves 4 for receiving coil windings by the use of a dicing blade saw or the like, as shown in FIG. 5. However, in order to fabricate magnetic heads having narrow tracks less than 30 .mu.m wide, it is required to narrow the spacings of the grooves 3 for defining the track width to extremely small dimensions, with the result that problems have arisen of lack of precision of the track width 2 and irregularities in shape due to chipping in the portions of the track width 2.
On the other hand, for metallic magnetic thin film heads comprising metallic magnetic thin films such as conventional Fe-Si-Al alloy, such magnetic materials have been utilized which are laminated to a predetermined film thickness by stacking such metallic magnetic films 3 to 10 .mu.m thick and non-magnetic insulation films about 0.5 .mu.m thick in alternating relation.
More specifically, in manufacturing such metallic magnetic thin-film head, the laminated magnetic material may be fabricated by sputtering films on a substrate to a thickness corresponding to the track width wherein the process for defining the track width is eliminated, whereby the problems involved in fabricating magnetic heads from a block-type core material as described above may be resolved.
However, it has been found through researches and experiments conducted by the present inventors that metallic magnetic films formed by sputtering have quite high internal stresses and that the laminated metal thin-film magnetic head made from such multi-layered magnetic material composed of metallic magnetic films, that is, magnetic core layers exhibits poor magnetic properties due to magnetostriction. More specifically, it has been found that such magnetostriction increases magnetically anisotropic energy in correlation with the internal stresses within the magnetic material of Fe-Si-Al alloy which is a soft magnetic material and that such soft magnetic material exhibits undesirable properties such as increased coercive force (coercivity) and poor permeability, so that it may not produce high output magnetic heads.
The common method of fabricating such metallic thin-film laminated magnetic head involves sputtering a metallic magnetic thin film on a substrate of a non-magnetic material such as glass or the like, laminating such films alternately with insulating layers, and bonding another non-magnetic substrate onto said laminates to sandwich the laminate between the opposed substrates to thereby form a magnetic core. However, studies by the present inventors have revealed that the film formation by sputtering is accompanied by the disadvantage that the substrates on which films have been sputtered are subject to warping due to internal stresses in the films, making it hard to provide uniform bonding throughout the bonding surfaces between the laminate and the substrates.
In the course of studying soft magnetic films of Fe-Si-Al alloy and further thin-film laminated magnetic heads fabricated by laminating soft magnetic films of Fe-Si-Al alloy and non-magnetic insulating films alternately, the present inventors have discovered that the soft magnetic films deposited by sputtering on a substrate has internal stresses generated therein which adversely affect the soft magnetic films, resulting in degrading the properties of the magnetic head. Further analysis of the internal stresses generated in such soft magnetic films has revealed that such internal stresses arise from not only thermal stresses due to differences in thermal expansion coefficient between the substrates and the films but also intrinsic stresses which are composed of compressive stresses generated in the films by the high energy particles sputtered from a target by Ar, impacting (peening) and penetrating into the film being deposited and of compressive stresses generated by the argon entrapped in the deposited films.
Furthermore, upon studying and experimenting on methods for relieving the films of internal stresses, the inventors have discovered that compressive stresses ascribed to peening may be removed during the process of heating the deposited magnetic film up to the heat treatment temperature and that compressive stresses caused by entrapped argon can be controlled by the amount of argon entrapped in the deposited film of Fe-Si-Al alloy within the range from 0.01 to 0.3 percent by weight and using substrates having a thermal expansion coefficient lower than that of the Fe-Si-Al alloy film.
The investors have also found the following factors important in effectively producing magnetic films substantially free from internal stresses:
(1) to employ a DC sputtering apparatus and apply RF bias to the substrate in order to control the amount of argon entrapped in the deposited film, PA1 (2) to use for a substrate a material having a thermal expansion coefficient lower than that of a film being deposited on the substrate, and PA1 (3) to subject a sputtered magnetic film of Fe-Si-Al alloy to heat treatment at a temperature of 450.degree. C. to 800.degree. C. The present invention is based on such novel knowledges.